Through neurophysiological experiments, we will determine how sensory responses and movement-related activity is dynamically altered during three types of purposeful hand movements. Specific Aim number 1 is to determine if somatosensory signals can be detected at times before movements when sensory gating is thought to occur, and if this detection depends on the modality of stimuli previously used to trigger movements. Specific Aim number 2 is designed to test changes in responsiveness gain before, during and after changes in visual feedback gain. Specific Aim number 3 is designed to test the modulation of sensory responsiveness with changes in the type of prior information about the task. Each experiment will determine when sensorimotor cortical neuronal activity is more tightly coupled to sensory stimuli and movement kinematics. Three hypotheses will be tested: that (1) Sensory stimuli requesting behavioral changes are less effective in altering movements if presented near movement onset or if other somatosensory stimuli have been presented previously, that (2) Sensory responses are better entrained to vibratory stimuli and movement-related activity is more tightly coupled to movement kinematics when the gain of visual feedback for movement to targets is abruptly changed, and that (3) Knowing where, but not in which direction, tracking-target deviations occur results, in suppression of most peripheral inputs that are time-locked to predicted tracking- target deviation onset, while knowing in which direction but not where (and thus when) a tracking-target deviation will occur results in a gradual increase the suppression of certain peripheral inputs. The under-lying central hypothesis is that external sensory information is utilized as needed to guide behavior and suppressed when redundant or competitive. These hypotheses will be tested, using single electrodes and possibly multi-electrode arrays to record extracellular activity in the primary somatosensory, parietal (area 5 and 7b), primary motor and premotor (PMd) cortices of awake, behaving monkeys trained to perform wrist movement tasks. Coupling of activity to sensory stimuli will be assessed by mean vector analyses. Movement kinematics will be correlated with neuronal activity using multiple regression analyses. The three behaviors to be studied could be used during retraining when sensory disorders occur following stroke, traumatic head injury, peripheral neuropathy and movement disorders. By understanding how and where somatosensory responsiveness is modified during behavior, deficits can be more readily assessed and localized.